Physical Evidence of Possible Arson
There are many physical clues that may suggest arson is a fire cause. They include:
For example, if a burned vehicle, reported stolen by the owner, is found in a deserted area with the key in the ignition switch, then it would obviously raise questions as to how the key was obtained by whoever “stole” the vehicle. In such a case, the owner may have been motivated to burn his or her vehicle to defraud the insurance company and get out of making payments on the vehicle. Likewise, if there had been no key and there was evidence of forced entry, then that would also be of interest. In this case, someone may have stolen the vehicle and then burned it to destroy evidence of theft.
The presence of accelerants, such as gasoline, which can sometimes be confirmed with analytical tests, is not always conclusive and must be used with caution. Most vehicles are powered by gasoline, and it is not necessarily unusual for someone to carry gasoline in a container in their car. It is also possible for inadvertent contamination to occur at the fire scene before a valid sample can me made. However, the use of an accelerant such as gasoline to start a fire can cause intense burns in carpeting and other combustible materials that can leave telltale patterns that should be considered when making the determination of cause.
In order for analytical tests for accelerants in carpet or other vehicle materials to be accurate, evidence handling is extremely important. This includes not only using the proper sampling and storage technique, but also the ability to gather samples and conduct testing in a timely fashion. Any material that may contain a flammable or ignitable liquid loses a quantity of the accelerant every day as it is exposed to weather. One source indicated that using an analytical technique called gas chromatography coupled with tandem mass spectrometry required that the proper sampling technique to be used within 17 days in order for the testing to be valid. Lesser techniques required even more prompt sampling, often within a few days .
Additional details on arson inspection techniques can be found in references 1-8.